hydra.go

// BSD 3-Clause License

// Copyright (c) 2021, Michael Grigoryan
// All rights reserved.

// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:

// 1. Redistributions of source code must retain the above copyright notice, this
//    list of conditions and the following disclaimer.

// 2. Redistributions in binary form must reproduce the above copyright notice,
//    this list of conditions and the following disclaimer in the documentation
//    and/or other materials provided with the distribution.

// 3. Neither the name of the copyright holder nor the names of its
//    contributors may be used to endorse or promote products derived from
//    this software without specific prior written permission.

// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
// DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
// CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
package hydra

import (
	"io/fs"
	"io/ioutil"
	"os"

	"github.com/caarlos0/env/v6"
	"github.com/go-playground/validator"
	"gopkg.in/yaml.v3"
)

var validate *validator.Validate = validator.New()

// This struct will initialize a new Hydra instance which will
// take care of handling your configuration.
type Hydra struct {
	Config Config
}

// This function will attempt to open, read and parse the file at the
// provided path into YAML.
func (h *Hydra) readAndParseYAML(path string, dst any) error {
	// Opening the file in readonly mode, to not cause accidental damage
	// to the configuration.
	f, err := os.OpenFile(path, os.O_RDONLY, fs.ModeTemporary)
	if err != nil {
		return err
	}

	c, err := ioutil.ReadAll(f)
	if err != nil {
		return err
	}

	// Parsing the environment variables specified in the
	// configuration struct and optionally assigning them
	// to unspecified fields.
	if err := env.Parse(dst); err != nil {
		return err
	}

	if path != "" {
		// Only parsing the configuration from the specified YAML
		// configuration file if a path was specified and matched.
		if err := yaml.Unmarshal(c, dst); err != nil {
			return err
		}
	}

	return nil
}

// This function will attempt to load all configuration variables
// both, from the environment and the YAML configuration file,
// which must be specified when initializing a `Hydra` struct.
func (h *Hydra) Load(dst any) (any, error) {
	// Getting the configuration path if it is supplied by the user.
	p, err := h.Config.findConfigPath()
	if err != nil {
		return nil, err
	}

	// If the configuration path was valid, provided and found parse
	// the YAML and unmarshal the output into the destination.
	if p != "" {
		if err := h.readAndParseYAML(p, dst); err != nil {
			return nil, err
		}
	}

	// The configuration will only be validated after being completely loaded.
	// Validations should be made according to the documentation at: https://github.com/go-playground/validator
	if err := validate.Struct(dst); err != nil {
		return nil, err
	}

	return dst, nil
}